Self-protecting bimetal member



1954 E. A. ERICSON 2,679,565

' SELF-PROTECTING BIMETAL MEMBER Filed Feb. 2, 1953 2 Sheets-Sheet 2 HIGH OVERLOAO Inventor: Eric A. Ericsoh,

His Attornes.

Patented May 25, 1954 UNITED STATES PTENT OFFICE 2,679,565 SELF-PROTECTING BIMETAL MEMBER Eric A. Ericson, Plainville, Conn., assignor to General Electric Company, a corporation 01' New York Application February 2, 1953, Serial No. 334,581 10 Claims. (01. 200116) air circuit breakers and the like. nected in series circuit relation with at least In certain applications, manually operable curone bimetallic protective arm, and so arranged rent responsively tripped air circuit breakers of that the protective arm is engaged by a therlow current rating, i e, of the order of ammally deformable member only upon the occurperes, are required to be sens1t1ve to compararence of a predetermined excessive ovelload curtively small amounts of overload current, for exin rent, and in such a manner as to shunt or short times the rated current. These requirements is spaced apart movable ends a pan of b1metall1c cannot ordinarily be met by elther the directly protective aims disposed in parallel spaced relaor induectly heated bimetalhc latch detents ordition and arranged to delorm nto engagement narily used in circuit breakers The indirectly with each other only upon the occurrence of a heated blmetals (1 e, having juxtaposed heatpredetermined excess ve overload current. The ing coils) are not sufficiently sensitive, and the protective arms and the bifurcated actuating arm directly heated bimeta s (i e, current carrying), are connected in series circuit relation and d while more sens1t1ve, are sub ect to permanent rectly heated by current conducted therethrough damage upon the passa e of short cl cuit curso that engagement of the ends of the protective ients of the magnitude contemplated For exarms short circuits the entlre bimetallic conample, if a directly heated bimetallic member is ducting path.

so proportioned that it will deflect to trip the My invention itself will be more fully underbreaker at an overload current of for example stood and its various objects and advantages order of one thousand times the rated current. tion with the accompanying drawing, in which of my invention to provide a directly current removed, of a manually operable current reresponsively heated bimetallic device which is sponsively tripped electric circuit breaker emsensitive to small amounts of overload currents bodying my invention and shown in the open and which includes additional current responsive 5 or oiT position; Fig. 2 is a similar View of the means for shunting the bimetal element upon same circuit breaker shown in the closed or the occurrence of a predetermined high overon position; Fig. 3 is a similar view of the same load current. circuit breaker shown in the trip free posi- It is another ob ect of my invention to protion; Fig 4 is a perspective View of the bimetallic vide a directly current responsively heated bilatching detent included in the circuit breaker metallic ovelload device which includes inteof Figs 1, 2 and 3 Figs 5 and 6 are side elegral thermally deformable means for shunting vational and plan views, respective y, of the b1- the thermal sens1t1ve element upon the occurmetallic member of Fig 4 showing the member rence of a predetermined high overload curin ts no load condltlon Flgs 7 and 8 ale simirent. lar side elevational and plan views, respectively, A still further object of my invention is the of the bimetallic member of Fig. 4. shown in its provision of a manually operable current reshort circuit condition; and Fig. 9 is a perspecponsively tripped circuit breaker including a ditive view of a bimetallic latching detent emrectly heated bimetallic latching detent for autobodymg my invention 1n difierent form and suitmatic tripping operation, which detent is sensi- 5 able for use in the circuit breaker of Figs. 1, 2 tive to small overload currents and includes addiand 3. tional thermal current responsive means for pro- Referring now to the drawings, and particutecting the bimetal against large short circuit larly to Figs. 1, 2 and 3, I have shown my invencurients. tion embodied in an air circuit breaker com- In carrying out my invention in one form I prising an open-sided housing 1 formed of suitable molded plastic insulating material and having recesses therein for the reception and retention of an operating mechanism. The housing is provided with a metal top plate 2 having return bent end portions 3 which seat in slots (not shown) in the housing. Within the return bent end portions 3 are disposed threaded nuts 4 adapted to receive bolts (not shown) for mounting the circuit breaker upon a panel or the like. The operating mechanism is adapted to be held in place in the housing I by a side cover plate (not shown), which is adapted to be connected to the housing by means of rivets passing through holes 5 in the housing i. The mounting nuts 4 are disclosed and claimed in my copending application Serial No. 342,633, filed on March 16, 1953, and assigned to the same assignee as the instant application.

Within the molded casing l is disposed a manual and automatic operating mechanism for a pair of cooperating switch contacts 6 and l. The contact 6 is stationary and is mounted upon a terminal member 8 projecting from the bottom of the casing i. The movable contact member 1 is mounted upon a movable switch member shown as an h shaped contact arm El pivotally mounted at a point intermediate its ends upon a fixed pivot pin iii carried by the casing l. The contact arm 9 is movable between an open circuit position, a fixed stop H formed on the casing, and a closed circuit position, shown at Fig. 2, where the contacts 6 and l are in engagement. A second terminal member i2 is seated in suitable positioning recesses in the housing I and projects from the bottom of the housing opposite the terminal member 8.

The L-shaped movable contact arm 9 is manually and automatically movable between open matically releasable toggle mechanism shown in the drawings in open, closed and tripped positions. The actuating mechanism, shown at Fig. 1 in its manual open position, comprises a releasable carrier member l3 pivotally mounted upon a fixed pivot M fixed in the casing i, and a pair of toggle links is; and i6 pivotally connected, respectively, to the upper ends of the carrier member it and the contact arm 9 by means of movable pivot pins We and its, respectively. The adjacent ends of the toggle links are pivoted together at their knee by means of a movable pivot pin H. The toggle link it is connected intermediate its ends to the pivot pin 16a, and thus includes a portion 16b extending beyond the pin 56a and engaging a compression spring IS, the other end of which is fixedly seated in a suitable recess in the casing l. The releasable carrier member is has mount ed thereon at its lower end a slidable latch mem ber 53a, biased to latching position by a spring i313 disposed between the latch member HM and a portion of the carrier member [3. The latch member 53c normally engages a thermo-responsive latching detent shown as a thermo-deformable bimetallic member I9 mounted in a recess in the lower part of casing I. As shown at Fig. l the latch i311 is withdrawn from the bimetallic member iii in the manual open position of the breakerby reason of a resetting bias exerted upon the toggle mechanism by the spring it as will be more fully explained hereinafter. At Fig. 2, however, it will be observed that when the mechanism is in its manual on or closed position, the latch Isa is in engagement with the bimetallic shown at Fig. l, where it engages and closed circuit positions by means of an automember i9, thereby normally to retain the carrier member it in fixed position. more fully explained hereinafter, the bimetallic latching detent i9 is connected in series circuit relation between the circuit breaker terminals 8 and I2 and carries the current passing through the breaker contacts 6 and 1. When sufliciently heated by the current the detent i9 deforms downwardly thereby to disengage the latch Na and release the carrier member 13 for movement to its tripped position shown at Fig. 3.

For manual opening and closing operation the circuit breaker is provided with a reciprocable actuating rod 20 supported for rectilinear movement in a collar 2% carried by the top plate 2 and having a stop shoulder Ziia which acts also as a dust seal when engaging the collar 2|. At its lower end the rod 28 carries a swingable connecting link 22, which is connected to the knee pivot pin ll of the toggle mechanism.

The operation of the foregoing circuit mechanism may now be observed in detail before proceeding with a further description of my new and improved bimetallic latching detent. In the manual open position of the breaker, as shown at Fig. l, the toggle formed by the links it and i6 is broken by movement of the actuating rod iii to its upper or withdrawn position. The toggle being broken, the compression spring It holds the contact arm 8 against the stop Ii and, because of the toggle link extension Nib, biases the link l5 clockwise about the pivot pin ifia, as shown in the drawing. With the contact arm El engaging the fixed stop the pivot pin Hie is held in position, so that clockwise rotation of the link 18 about the pin IBa (within the limit of movement permitted by the swinging link 22), draws the toggle links i5 slightly to the right as shown in the drawing and rotates the carrier member E3 to a slightly withdrawn or reset position, as shown at Fig. 1.

When the actuating rod 20 is depressed, as shown at Fig. 2, until its stop shoulder 20a engages the collar 2 I the knee pivot pin I1 is moved downwardly, thereby to extend the toggle links 15 and i6 and move the knee pivot pin I! across the line of action of the spring IE to a slightly overset position as shown at Fig. 2. Further movement of the knee pivot pin I1 is prevented by engagement of the actuating rod shoulder Zfia with the collar 2 i. In this position the shoulder Mia acts as a dust seal for the casing i. In this straightening movement the toggle links 15 and it force the pivot pins liia and 18a apart. Movement of the pivot pin 511 is limited by engagement of the latch member i311 with the bimetallic latching detent l9, so that the pivot pin ifia in the normal unreleased position of the carrier member 153 acts substantially a a fixed pivot. Thus the straightening oi" the toggle links l5 and it serves principally to move the pivot pin [6a to the right, thereby to rotate the contact arm 8 clockwise about its fixed pivot pin H3 and bring the contacts 6 and 'i into engagement. In this position of the mechanism, the knee pivot pin I1 is slightly below the line of action of the spring l8, so that the pressure of the spring it retains the toggle in its overset position. In this position the spring 18 also tends tomove the entire toggle mechanism to the left, as shown in the drawing and longitudinally of the extended toggle links Rectilinear movement of the entire toggle mecha nism to the left is restrained, however, by latch ing of the carrier member 13, and thus retentioi of the pivot pin 15a in a normal fixed position.

breaker It will now be understood that reverse manual movement of the actuating rod 20, by withdrawcollapses the toggle links H) and I6 and restores the mechanism to the open position of Fig. 1.

If, with the circuit breaker in the on posilatch is, extended the pressure of the spring 18 upon the toggle links I and [5 moves the links actuating This renders the breaker trip free in operation, in that the contacts are automatically separated by rethe link extension Nib, being rotated slightly movement, has lowered the line of action of the spring slightly. The

& now being against the stop I I to hold the pivot pin Ifia. against movement, the links extension l 6b converts the pressure of spring l8 to a torque tending to rotate the link it clockwise about the Thus, if the actuating button is released from the position shown at Fig. 3, the compression spring l8 will break the toggle and move the actuating rod 20 upwardly to its open position by rotating the link It clockwise about the pivot pin 501. In so rotating the link It draws the link !5 to the right and by this action rotates the carries l3 clockwise about its pivot pending application Serial No. 331,558, filed on January 16, 1953, jointly by me and Raymond N. Rowe and assigned to the same assignee as the instant application.

Referring now more particularly to the bi metallic latching detent til, I have shown at Fig. 4, a perspective view of this detent mounted upon an offset metal base member fixed in the easing I.

The bimetallic member It comprises a bifurcated bimetallic actuating arm 26 including two spaced apart coplanar actuating fingers 26a and at its bight upon the supporting member 25, as by welding. The free ends of the actuating fingers 26d and 261) are connected together by a detent tip 2'! of insulating material, the tip 21 being engaged in operation by the latch member I 3a as shown at Fig. 2. The tip 21 i of insulating material to prevent shortcireuiting of the bimetal strip l9 through the metal actuated linkage. The actuating fingers tive arms 28a and 2812'. While these protective arms may be separate pieces fixed to the actuating fingers they are preferably formed as shown as integral reversely directed extensions of the actuating fingers 26d and 2th, and are turned over laterally so that they lie in planes perpendicular to the plane of the parallel spaced relation with each other.

The protective bimetallic arms 28a and 28b are arranged to be deformed toward engagement with each other when heated. invention shown at Figs. 1 to 8 this is accomplished by providing the relatively high expansion metal on the tops of the arms 28a and 25b, and thus on the outsides of the protective arms arms 23c and 2% contact tips 29a and 2% respectively, which tips are sufiiciently spaced apart under no-load conditions that they do not come into engagement with each other except upon the occurrence of predetermined excessive overload currents.

To connect the bimetallic device it in series circuit relation between the circuit breaker terminals t and I2, the contact carrying ends of the protective arms Eta and 28b are provided with flexible electric conductors or pigtails 30a and Bilb respectively, between which the actuating fingers 25c and 26b and the protective arms 28a and. 28b are connected in series circuit relation. As shown in i the pigtail 36a is connected to the movable contact arm 9, while the pigtail 3% (not the finger 26a, the finger 2612, the arm 2% to the pigtail till), or the reverse.

The bimetallic member of Fig. 4; is shown in plan and elevation view in its no load condition at Figs. 5 and 6, the detent tip 21 and the mounting base 25 being omitted.

Referring now again to Figs. 1, 2 and 3, it will be observed that the bimetallic member !9 is so For normal overloads of the order of several times up to ten or twenty times normal current, deformation of the protective arms 28a and 28b is insuificient to bring the contacts 25a and 29b into engagement. The normal spacing adjustment of the contacts 251a. and 2% howa short circuit path between the pigtails 30a and 30b and shunting the entire bimetallic member .19 out of is before the protective arms come into engagement. In practice it has been found that the carrier member I3 is released and the protective arms engaged before the short circuit current (which may be an arcing current) through the circuit breaker contacts 6 and l attains its maximum value. In this way the bimetallic member is protected against the carrying of excessive short circuit currents.

At Fig. 9 I have shown another form of selfprotecting bimetallic detent comprising a bimetallic actuating arm 35, mounted at one end upon a supporting base and engaging at its other end a latch indicated. as the latch 13a of Figs. 1, 2 and 3. Mounted also upon the base member 36 between the bimetallic arm 35 and the member 36, and in substantially parallel spaced relation with the arm 35, there is provided a bimetallic protective arm 3d carrying at its end a contact tip 39 engageable with a cooperating contact 40 on the end of the bimetallic actuating arm 35. The contacts 3% and to are normally spaced apart. Both the bimetallic actuating arm 35 and the bimetallic protecting arm 38 are arranged to deform downwardly, as shown in the drawing, when heated. The actuating arm 35, however, is of reduced cross section and is therefore heated to a greater extent by a current of any given value, so that the arm 35 moves downwardly at a greater rate than the arm 38. Current is conducted through the arms 35 and 38 in series circuit relation between a pair of flexible electrical conductors or pigtails ti and 42 connected respectively to the free ends of the arms 38 and 35.

In operation the bimetallic overload device of Fig. 9 operates to release the latch ita upon small overload currents without engaging the contacts 39 and t8, the contact as moving in the same direction as the contact 40 but at a lesser rate. Upon the occurrence of a predetermined excessive overload current, however, the rate of movement of the contact it becomes so great that it overtakes the contact 33 and brings the contact into engagement, thereby to shunt the arms 35 and 38 out of the circuit.

It may now be noted that the thermally responsive protective arms characterizing my invention normally carry current. These arms, being near the actuating arm, act to supplement the heating of the actuating arm. This is of considerable advantage in a bimetal of low current response where it is difficult to obtain sufficient heating without unduly reducing the cross section of the bimetal.

While I have described only certain preferred embodiments of my invention by way of illustration, many modifications will occur to those skilled in the art, and I therefore wish to have it understood that I intend in the appended claims to cover all such modifications as fall within the true spirit and scope of my invention.

What I claim as new and desire to secure by Letters Patent of the United States is:

1. In a directly current responsively heated electric overload device, a thermally deformable bimetallic actuating arm adapted to be heated by current conducted therethrough, and additional thermally deformable means, movable in response to current traversing said actuating arm and establish a short circuit around said actuating arm upon the passage of a predetermined excessive current through said actuating arm.

2. In a directly current responsively heated electric overload device, a thermally deformable bimetallic actuating arm adapted to be heated by current conducted therethrough, and a sec- 0nd thermally deformable bimetallic arm connected in series circuit relation with said actuating arm and carrying at its end a contact movable therewith to establish a short circuit around said actuating arm upon the passage of a predetermined excessive current therethrough.

3. In a directly current responsively heated electric overload device, a thermally deformable bimetallic actuating arm adapted to be heated by current conducted therethrough, and a bimetallic protective arm mounted upon said actuating arm and connected in series circuit relation therewith, a contact carried by said actuating arm and disposed for engagement with said protective arm, said protective arm being deformable into engagement with said contact thereby to short circuit said actuating arm only in response to the passage of a predetermined excessive current through said bimetallic arm.

4. In a directly current responsively heated electric overload device, a pair of bimetallic actuating fingers mounted at one end in parallel coplanar relation and adapted to be heated by current conducted therethrough, and a pair of bimetallic proteotive arms mounted upon the free ends of said actuating fingers and disposed for thermal deformation into engagement with each other, said protective arms being connected in series circuit relation with said actuating fingers and engaging each other only upon the passage of a predetermined excessive current through said fingers thereby to short circuit said fingers.

5. In a directly current responsively heated electric overload device, a bifurcated bimetallic actuating arm mounted at its bight and having its movable ends disposed in spaced apart coplanar relation, said movable ends being thermally deformable in a direction perpendicular to the plane thereof in response to electric current conducted therethrough, and a pair of bimetallic protective arms mounted upon the free ends of said actuating arm and disposed in parallel spaced relation with each other, said protective arms being connected in series circuit relation with said bifurcated actuating arm and being thermally deformable in opposite directions perpendicular to the direction of movement of said actuating arm and into engagement with each other, said protective arms remaining spaced apart in normal overload operation and engaging at their ends to short circuit said actuating arm only upon the passage of a predetermined excessive current through said arm.

6. In a directly current responsively heated electric overload device, a bifurcated bimetallic actuating arm mounted at one end with its other end movable perpendicular to the plane thereof, a pair of bimetallic protective arms mounted upon the spaced apart ends of said bifurcated actuating arm and disposed in parallel spaced relation for movement toward and away from each other along a line perpendicular to the direction of movement of said actuating arm, said protective arms being connected in series circuit relation with said bifurcated actuating arm and all said arms being adapted to be heated by current conducted therethrough, the ends of said protective arms being deformable into engagement with each other thereby to short circui' said actuating arm only upon the occurrence 0 a predetermined excessive current through sail arms.

'7. In a directly current responsively heate electric overload device, a bimetallic actuatin arm mounted at one end and having its free en movable in response to current conducted thereseries circuit relation with said contacts for through, a resilient protective arm mounted in direct heating by current conducted through said substantially parallel spaced relation with said arm, and thermally deformable means movable actuating arm and having at its free end a conin response to current through said actuating arm tact engageable with the free end of said actuand establishing a circuit around said actuatlng ating arm said actuating arm deforming sufiiarm upon the passage of a predetermined excesciently to engage said protective arm only upon sive current therethrough.

the passage of a predetermined excessive current 10. In a current responsively tripped electric therethrough, thereby to short circuit said actucircuit breaker, a pair of relatively movable ating arm. 1 cooperating switch contacts, manually operable through, a bimetallic protective arm mounted in bifurcated bimetallic actuating arm mounted at circuit relation and being thermally deformable said bifurcated actuating arm and disposed for in the same direction and at different rates, said thermal deformation into engagement with each protective arm being movable at a lesser rate than other, said protective arms and said bifurcated said actuating arm whereby the free end of said actuating arm being connected in series circuit actuating arm engages the free end of said prorelation with said contacts for direct heating in tective arm only upon the passage of a predeterresponse to current conducted therethrough and 9. In a current responsively tripped electric arm only upon the passage of a predetermined circuit breaker, a pair of relatively movable excessive current through said arm. cooperating switch contacts, manually operable mechanism for opening and closing said con- References Cited in the file of this patent tacts, said mechanism including a movable latch UNITED STATES PATENTS member releasable to automatically separate said contacts, a latching detent having a thermally Number N Date deformable bimetallic actuating arm normally 2,412,483 Warrmgton 10) 1946 engaging said latch member to restrain its move- 2587342 Lmcks et 26, 1952 ment, said actuating arm being connected in 25091466 Blonder sept- 2, 1952 

